Filter



July 21, 1936.

Original Filed Sept. 24, 1931 INVENTOR- CLARENC W.HANSELL ATTORNEY- Patented July 21, 1936 UNITED STATES FILTER Clarence W. Hansel], Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Original application September 24, 1931, Serial t No. 564,770. Divided tober 19, 1932, Serial 2 Claims.

This application is a division of my copending application Serial Number 564,770, filed September 24, 1931.

In general my present application relates to filter circuits and has as an object the provision of an improved filter circuit utilizing circuits having either lumped inductances and capacity or uniformly distributed inductances and capacities.

A further and more important object of my present invention is to provide a filtering arrangement utilizing filter elements having inductance and capacity which filter elements have overlapping resonance curves and which are so connected together as to pass with equal facility frequencies of the overlapping range as well as those adjacent thereto.

While I have attempted to define my present invention with particularity in the appended claims, it may best be understood both as to its structural organization and mode of operation by referring to the accompanying drawing wherein,

Figure 1 illustrates my improved filtering circuit utilizing lumped inductors and capacitors;

Figure 2 illustrates a modification thereof utilizing filter circuit elements having uniformly distributed inductance and capacity; and,

Figure 3 is a series of resonance curves explanatory of my present invention.

Referring to Figure 1 the series resonant circuits l8a', 20a have overlapping resonance curves as described in my copending application. Similarly, series tuned circuit 23a consisting as shown of a lumped inductor and a lumped capacitor has a resonance curve overlapping series tuned circuit 20a. Series tuned circuit I941 overlaps the curve of series tuned circuit l8a. The overlapping resonance curves are illustrated in Figure 3.

The alternating output circuit 50 is connected between the conductive connection 34 connecting one terminal of the series tuned circuit together and the point intermediate the ends, preferably at a point of zero alternating potential of input coil 28. This coil connects the other ends of the tuned circuits Mia and 20a in phase opposition as well as connecting circuits 23a, 20a, and la, I 9a. in phase opposition which pairs of circuits have overlapping characteristic curves.

If a wider pass band is desired any number of series tuned circuits such as illustrated having and this application Oc- No. 638,476

lumped inductors and lumped capacitors may be used provided, however, that the circuits for adjacent frequencies are connected to opposite sides of the filter input circuit.

In Figure 2 I have shown the application of resonant sections of transmission lines, having uniformly distributed inductance and capacity, for providing a filter coupling between two circuits 2B, 50 either one of which may be considered the input circuit and the other an output circuit. The lines 84, 86 are adjusted in length so as to be resonant on opposite sides of a mean frequency which it is desired to transmit between the two circuits 28, 50.

In my claims where I speak of connecting the filter circuit elements cophasally or in phase opposition it is to be understood that I refer to the phase conditions which would correspond to resonance of the elements. Since the elements will not be resonant for the same frequencies and their currents change phase as the frequency is changed it must be understood that I have used the expressions cophasally and in phase opposition for want of more expressive language.

Having thus described my invention, what I claim is:

1. A filter circuit comprising a number of transmission lines joining an input and output circuit, said transmission lines forming resonant circuits with overlapping resonance curves, a low impedance connection connecting together terminals of said lines, a reactive circuit connected between other terminals of said lines, a circuit coupled to said reactive circuit, and a circuit connected to a point intermediate said reactive circuit and to said low impedance connection, said filter circuit acting to transmit with equal intensity electrical energy in the frequency band between and including the resonant frequencies of said lines with equal intensity.

2. A filter circuit comprising two transmission lines having uniformly distributed inductance and capacity, an input circuit coupled to a pair of terminals of said lines, an output circuit coupled to another pair of terminals of said lines, and means for adjusting the length of said transmission line so as to be resonant on opposite sides of a mean frequency which is desired to be transmitted between said input and output circuits.

CLARENCE W. HANSELL. 

